Because covid hasn’t been prevalent in this part of the country for years, and people in the area haven’t shown to be infected with it. The positive results in these mink are leading some scientists to conclude that there’s a source of covid in the wild.
Between September to January of this year, mink in three Polish farms tested positive for the pandemic coronavirus, SARS-CoV-2— presenting a concerning mystery as to how the animals became infected.
Further Reading
Mink variant of coronavirus spreads to humans in Denmark; full cull planned
SARS-CoV-2 infections in mink aren’t particularly noteworthy or concerning on their own; it’s well established that mink are susceptible to the virus. The realization early in the pandemic resulted in extensive culls in Denmark and the Netherlands during 2020 and led to intensive monitoring and regulation of remaining mink herds in many places, including Poland.
But the recent cases in Polish mink , reported this week in the journal Eurosurveillance, are unusual. While previous mink outbreaks have linked to infected farmworkers and local circulation of the virus—indicating human-to-mink spread—none of the farm workers or families in the recently affected farms tested positive for the virus. In fact, health investigators found that the infected mink carried a strain of SARS-CoV-2 that has not been seen in humans in the region in more than two years (B.1.1.307).
The finding suggests that humans were not responsible for infecting the mink—at least not directly. Rather, it suggests that another unknown species may have been stealthily harboring and spreading the otherwise bygone strain for some time and managed to carry it onto the mink farms.
The suggestion raises more concern over viral “spillback.” The term relates to the more recognized “spillover,” when a virus jumps from a host population—a reservoir—to a new population, such as humans. SARS-CoV-2 is thought to have originated in a reservoir of horseshoe bats before it reached humans. Since then, it is clear that it can also infect a broad range of animals, including rodents, cats, dogs, white-tail deer, non-human primates, as well as ferrets and mink. Researchers fear that the virus could spill back to an animal population that could become a new reservoir from which the virus could periodically move back to humans.
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